This new era will be defined by the pervasiveness of human environmental impacts, including changes to Earth's soils and surface geology, proponents of the theory say.

"Unquestionably we are entering the Anthropocene," said Daniel Richter of Duke University, who authored the new study of Earth's changing soils.

In the December 2007 issue of the journal Soil Science, Richter warns that Earth's soils already show a reduced capacity to support biodiversity and agricultural production.

As the amount of depleted and damaged soils increases, global cycles of water, carbon, nitrogen, and other materials are also being affected.

Richter's report supports an independent proposal in the current issue of the journal GSA Today that calls for official recognition of the Anthropocene epoch.

In that paper, Jan Zalaseiwicz of the University of Leicester in England and colleagues argue that the fossil and geologic record of our time will leave distinct signatures that will be apparent far into the future.

To future geologists, Zalaseiwicz said, "the Anthropocene will appear about as suddenly as [the transition] triggered by the meteorite impact at the end of the Cretaceous" 65.5 million years ago, when the dinosaurs became extinct.

Overworked Earth

Today about 50 percent of the world's soils are subject to direct management by humans.